Colour Doppler induced streaming: an indicator of the liquid nature of lesions

As sound waves traverse tissue, interaction with reflecting or absorbing obstacles results in a transfer of momentum from the wave to the medium. This generates a local force in the direction of propagation. If this occurs in a fluid medium, sufficient pressure may be generated to cause flow-"streaming". Generally, it is difficult to demonstrate this streaming in images using the usual diagnostic B-mode intensities, but the increased intensities in a colour Doppler (or power) region of interest enhance the phenomenon. This allows streaming to be both visualized by the motion of small particles and detected by colour change on the colour Doppler B-mode image. Borders of streaming between the simple grey scale image and the colour region may be easily seen, with retrograde flow in the regions subjected to a lower intensity. This phenomenon has been demonstrated in ocular, scrotal, thyroid, breast, ovarian and inflammatory collections or lesions, confirming the liquid nature, occasionally of fluid which is very echogenic due to contained debris. The technique is recommended as another tool which is available to most general ultrasound departments and will assist in the characterization of tissue.